Various known techniques were proposed for improving the electrical properties of biocompatible electrodes. For example, in “An Electrode for Recording Single Motor Unit Activity during Strong Muscle Contractions,” IEEE Transactions on Biomedical Engineering, Vol. BME-19, No. 5, September, 1972, pages 367-372, De Luca and Forrest describe the construction of a lightweight needle electrode offering four monopolar and six bipolar microelectrode combinations. An electrolytic treatment for reducing the impedance of the electrode is described. The frequency response of twelve monopolar and twelve bipolar microelectrodes was measured before the electrolytic treatment, ten minutes after the electrolytic treatment, and 72 hours after the electrolytic treatment. The Bode form was used to synthesize a simple resistance-capacitance (RC) model for each of the three situations, giving some insight to the physical change at the tip of the electrode. As another example, in “Comparison of Electrode Impedances of Pt, PtIr (10% Ir) and Ir-AIROF Electrodes Used in Electrophysiological Experiments,” Medical & Biological Engineering & Computing, January, 1982, volume 20, pages 77-83, Gielen and Bergveld describe tissue impedance measurements with four-electrode assembly, encountered by unexpected difficulties because of a combination of electrode impedance and stray capacitance in the array of four electrodes, which could lead to serious measuring failures in the low-frequency range. The publication describes using electrolytic etching to enlarge the effective surface of electrodes, resulting in lower electrode impedances. The etching was achieved by applying a sinusoidal voltage between the electrode and a large indifferent Pt-ring electrode both immersed in a saline solution.
U.S. Pat. No. 4,721,551 describes a method for electroplating iridium metal onto the surface of a metallic microelectrode for use in a biomedical prosthetic device. Another aspect of the method discloses conditioning the microelectrode by storage for between about 6 and 150 hours in a physiologically equivalent phosphate buffered saline solution selected under in vitro conditions. Further conditioning of the microelectrode is done by applying between about positive 1 and negative 1 volts for between 100 and 10,000 millivolts per second, for between about 1 and 100 cycles to form at least one iridium oxide on the surface of the microelectrode.